Circadian rhythms have an influence on human performance. Interleukin-6 is a cytokine which plays a role in muscle energy homeostasis during physical exercise. This study tested the effect of diurnal variation and alpha-lipoic acid, a natural thiol antioxidant, on skeletal muscle contractile properties, interleukin-6 response and oxidative damage. Male subjects (n=26) performed isokinetic exercise in different time-of-day. Next, the subjects were supplemented with alpha-lipoic acid for two weeks and the exercise tests were repeated. Blood samples were analyzed at baseline and immediately after exercise. Leg extensor muscle parameters were compared withtime-of-day. Maximal work per single repetition and total work values were higher in the afternoon time, suggesting a time-of-day effect. Serum interleukin-6 levels increased in response to exercise, but were not associated with time-of-day. Alpha-lipoic acid did not have a significant effect on any of the measured parameters. Diurnal variations during exhaustive eccentric exercise seem to reflect muscle contractile work capacity. Exercise increases serum interleukin-6 levels irrespective of diurnal variation.
Key words: Diurnal variation, lipoic acid, interleukin-6, muscle performance.
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